1. Field of the Invention
The present invention relates to a broadcast wave receiving apparatus, and more particularly to a broadcast wave receiving apparatus for selectively receiving a plurality of broadcast waves while performing the detection of the broadcast waves.
2. Description of the Related Art
Up until now, there have been proposed a wide variety of broadcast wave receiving apparatus of this type one typical example of which is disclosed in Japanese Patent Laying-Open Publication No. H08-18405.
The conventional broadcast wave receiving apparatus 80 comprises an antenna 81 having passed therethrough a plurality of broadcast waves each having information on an audio wave. The broadcast waves are respectively oscillated at specific frequencies different from one another.
The conventional broadcast wave receiving apparatus 80 further comprises a tuning circuit 82 having a resonance frequency electronically tunable to each of the specific frequencies, and a microcomputer unit 86 for controlling the tuning circuit 82 to ensure that the resonance frequency of the tuning circuit 82 is tuned to the specific frequency before allowing the tuning circuit 82 to produce a broadcast signal indicative of the broadcast wave at the specific frequency.
The conventional broadcast wave receiving apparatus 80 further comprises a demodulating unit 87, a mute circuit 85, an amplifier unit 83, and a speaker unit 84. The demodulating unit 87 is adapted to produce an audio signal indicative of the audio wave from the broadcast signal produced by the tuning circuit 82. The mute circuit 85 is adapted to assume two different operation state consisting of a first operation state to have the amplifier unit 16 receive the audio signal from the tuning circuit 82, and a second operation state to have the amplifier unit 16 fail to receive the audio signal from the tuning circuit 82. The amplifier unit 83 is adapted to amplify the audio signal produced by the tuning circuit 82, while the speaker unit 84 is adapted to produce an audio sound to be represented by the audio signal produced by the tuning circuit 82.
When the microcomputer unit 86 is operated to control the tuning circuit 82 to ensure that the resonance frequency of the tuning circuit 82 is electronically and automatically tuned to each of the specific frequencies under the condition that the audio signal is produced from the broadcast wave detected at the specific frequency “f1” by the tuning circuit 82, the audio signal produced by the tuning circuit 82 firstly fails to be outputted to the amplifier unit 83 by the mute circuit 85 in the step S91.
The microcomputer unit 86 is then operated to produce information on the updated specific frequency equal to the addition of the specific frequency “f1” and the increment “f2” in the step S92. The microcomputer unit 86 is then operated to control the tuning circuit 82 to ensure that the resonance frequency of the tuning circuit 82 is tuned to the updated specific frequency “f1” before allowing the tuning circuit 82 to detect the broadcast wave which is oscillated at the updated specific frequency “f1” in the step S93.
The microcomputer unit 86 is then operated to judge whether or not the electric field intensity “Vf” of the broadcast wave detected by the tuning circuit 82 is smaller than the predetermined threshold level “V” in the step S94.
When the answer in the step S94 is affirmative “YES”, i.e., the electric field intensity “Vf” of the broadcast wave detected by the tuning circuit 82 is smaller than the predetermined threshold level “V”, the step S94 proceeds to the step S92. When, on the other hand, the answer in the step S94 is negative “NO”, i.e., the electric field intensity “Vf” of the broadcast wave detected by the tuning circuit 82 is not smaller than the predetermined threshold level “V”, the judgment is made by the microcomputer unit 86 whether or not the intermediate signal which is oscillated at the intermediate frequency exists in the broadcast signal indicative of the broadcast wave detected by the tuning circuit 82 in the step S95.
When the answer in the step S95 is affirmative “YES”, i.e., the intermediate signal which is oscillated at the intermediate frequency exists in the broadcast signal, the audio signal produced from the broadcast wave is outputted to the amplifier unit 83 by the mute circuit 85. When, on the other hand, the answer in the step S95 is negative “NO”, i.e., the intermediate signal which is oscillated at the intermediate frequency does not exist in the broadcast signal, the step S95 proceeds to the step S92.
The conventional broadcast wave receiving apparatus, however, encounters such a problem that the audio sound fails to be produced from the broadcast wave while the detection of the broadcast waves is performed by the microcomputer unit.